Ozone ($\text{O}_3$) causes characteristic leaf curling, chlorosis (yellowing), and necrosis in sensitive plant species. Ground-level ozone (a secondary pollutant formed from NOₓ and VOCs in sunlight) enters leaves through stomata and causes oxidative damage to cell membranes, disrupting photosynthesis. $\text{SO}_2$ causes bleaching and marginal necrosis; $\text{CO}$ has less direct phytotoxic effect; $\text{H}_2\text{S}$ causes stomatal closure.